Abstract

The operation of many existing gas sensors relies on the chemisorption or physisorption of gas molecules on their sensing materials. However, the non-specific nature of adsorption results in poor selectivity of gas sensors, which can cause wrong detection. This issue is usually tackled by using a gas sensor array, whose individual elements have different selectivities. The diverse selectivity enables the sensor array to produce unique response patterns, which can be used for subsequent gas identification. This approach is effective but is also complex and costly. In this thesis, we proposed an innovative dual transduction technique to achieve single sensor gas identification. It combines gravimetric and resistive transduction on a single sensor. The gas identification is enabled by the relationships between the gravimetric and resistive responses that are unique to different target gases. The dual transduction gas sensing was firstly implemented by integrating film bulk acoustic resonators (FBAR) with interdigitated electrodes (IDE). The gas-induced mass variation of the sensing material is detected through the resonating frequency shift of the FBAR while the resistance change is detected through the IDE. Through the design of a configurable readout circuit, dual transduction was also implemented on a single port surface acoustic wave (SAW) resonator. Compared to the FBAR implementation, the fabrication process of dual transduction SAW gas sensor is much simpler, which makes it more cost-effective and reliable. Nevertheless, FBAR is advantageous in terms of device size. Besides single sensor gas identification, the proposed approach can also improve the overall limit of detection (LOD) to different gases by exploiting the individual responses with the best LODs. Although the dual transduction gas sensors can achieve single sensor gas identification, its accuracy will decrease when the types of VOCs to be identified increase. This problem was solved by combining the dual transduction technique with the sensor array method. Compared to the conventional gas sensor arrays, the dual transduction gas sensor array collects more information from the sensing materials and can thus achieve better gas identification performance.